1. Field of the Invention
The present invention relates to a receiver applied to a television set for receiving a digital broadcast.
2. Description of the Related Art
Conventionally, television broadcasting has been conducted by means of analog broadcasting. In analog broadcasting, one program is broadcast by only one physical channel. In this case, the physical channel is defined as a frequency band of carrier waves used for broadcasting a program. By a receiver (for example, a television set) of analog broadcasting, a channel to be received is switched by switching a frequency to be received.
In the conventional receiver, there is provided a channel-up/channel-down function by which a channel, in which a program is being broadcast, is successively switched in the order of increasing or decreasing the channel number so that a user can easily tune in to the program. In this case, the channel-up/channel-down function operates as follows. A channel in which a program is being broadcast is previously detected with respect to all frequency bands capable of being received. According to a channel map on which the channel, in which it is detected that the program is being broadcast, is registered, the channel in which the program is being broadcast (the channel registered on the channel map) is successively switched in the order of increasing or decreasing the channel number.
In a common receiver, there is provided a function of scanning an overall region by which a channel, in which a program is being broadcast, is automatically detected and registered on a channel map with respect to all frequency region capable of being received. Also, there is provided a function (one of OSD (On Screen Display) functions) of registering onto and deleting from the channel map by the unit of a physical channel. When the above OSD function is utilized, it is possible for a user to register only his favorite channels on the channel map and tune in to only his favorite channels by using the channel-up/channel-down function. There is proposed a channel preset device by which tuning can be easily conducted in the multiple channel broadcast (Japanese Unexamined Patent Publication No. 2000-101939).
Recently, digital broadcasting, in which a plurality of programs can be broadcast by one physical channel, for example, digital broadcasting by Advanced Television Standards Committee System (ATSC system) has started. In digital broadcasting, a plurality of multiplex virtual channels are formed in a physical channel, and a program is broadcast for each virtual channel. That is, in the case of digital broadcasting, it is possible to broadcast a plurality of programs by one physical channel. Concerning the receiver of digital broadcasting, it is proposed to provide the above channel-up/channel-down function so that a program can be easily selected.
In this connection, in the case of digital broadcasting, a plurality of programs are broadcast by one physical channel. Accordingly, there are provided two channel numbers. One is a physical channel number showing a physical channel, and the other is a virtual channel number showing a multiplex virtual channel. The virtual channel number includes a main channel and sub-channel. A receiving channel is selected in the virtual channel (main channel and subchannel).
However, on the channel map applied to the conventional receiver, registration and deletion are conducted by the unit of a physical channel. Therefore, the following problems may be encountered. In the case of digital broadcasting in which a plurality of programs are broadcast in one physical channel, a channel (sub-channel), in which a program a user does not like is being broadcast, is registered. On the contrary, when a channel (sub-channel), in which a program a user does not like is being broadcast, is deleted, a channel (subchannel), in which a program the user likes is deleted. Accordingly, it is impossible for the user to register only programs he likes on the channel map. Therefore, it is impossible for the user to tune in to his favorite channel by the channel-up/channel-down function.